1. Field of the Invention
The present invention relates to fuels, particularly gasoline fuels which are substantially free of oxygenates. More specifically, the present invention relates to a low-emission gasoline fuel which, upon combustion in a spark-ignited engine, provides surprisingly low emissions, particularly of nitrogen oxide emissions, and is also substantially free of oxygen-containing compounds.
2. Brief Description of the Prior Art
One of the major environmental problems confronting the United States and other countries is atmospheric pollution caused by the emission of pollutants in the exhaust gases and gasoline vapor emissions from gasoline fueled automobiles. This problem is especially acute in major metropolitan areas where atmospheric conditions and the great number of automobiles result in aggravated conditions. While vehicle emissions have been reduced substantially, air quality still needs improvement. The result has been that regulations have been passed to further reduce such emissions by controlling the composition of gasoline fuels. These specially formulated, low emission gasolines are often referred to as reformulated gasolines. In California, low emissions gasoline is often referred to as California Phase 2 gasoline. One of the requirements of these gasoline regulations is that, in certain geographic areas, oxygen-containing hydrocarbons, or oxygenates, be blended into the fuel.
Congress and regulatory authorities, such as CARB (the California Air Resources Board), have focused on setting specifications for low emissions, reformulated gasoline. The specifications, however, require the presence of oxygenates in gasoline sold in areas that are not in compliance with federal ambient air quality standards for ozone, and the degree of non-attainment is classified as severe, or extreme. Among the emissions which the reformulated gasoline is designed to reduce, are nitrogen oxides (NOx), hydrocarbons (HC), and toxics (benzene, 1,3-butadiene, formaldehyde and acetaldehyde). A reduction in these emissions has been targeted due to their obvious impact upon the air we breathe and the environment in general.
There is increasing attention from environmental agencies regarding the need for a reduction in emissions of nitrogen oxides. NOx emissions are known precursors for smog created in metropolitan areas. Most of the NOx emissions are man-made, with gasoline fueled engines generating about 24% of the man-made NOx emissions. NO is the major constituent of NOx emissions from combustion processes. NO is a precursor of NO2 in the atmosphere and a critical constituent in the formation of ozone. NO2 can irritate the lungs and reduce respiratory function. NOx can be an important precursor to secondary formation of particulates, according to the xe2x80x9cNational Air Quality and Emission Trends Report,xe2x80x9d 1992, Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, EPA 454/R-93-031, October 1993. A reduction of nitrogen oxides, particularly in large metropolitan areas such as Los Angeles and Sacramento, Calif., and many eastern U.S. states, would be most valuable. As a consequence of all these harmful effects, the reformulated gasolines have been designed to reduce NOx emissions.
Oxygenated gasoline is a mixture of conventional hydrocarbon-based gasoline and one or more oxygenates. Oxygenates are combustible liquids which are made up of carbon, hydrogen and oxygen. All the current oxygenates used in reformulated gasolines belong to one of two classes of organic molecules: alcohols and ethers. The Environmental Protection Agency regulates which oxygenates can be added to gasoline and in what amounts.
The primary oxygen-containing compound employed in gasoline fuels today is methyl tertiary butyl ether (MTBE). While oxygen is in most cases required in reformulated gasolines to help effect low emissions, the presence of oxygenates in gasoline fuels has begun to raise legitimate environmental concerns. For example, the oxygenate methyl tertiary butyl ether has been observed in drinking water reservoirs, and in a few instances, ground water in certain areas of California. As a result, the public is beginning to question the benefits and/or importance of having cleaner burning gasolines, if they simply pollute the environment in other ways. Furthermore, oxygenates also have a lower thermal energy content than non-oxygenated hydrocarbons, and therefore reduce the fuel economy of gasoline fueled motor vehicles.
Thus, while some of the concerns with regard to gasoline fuels containing oxygenates, such as methyl tertiary butyl ether, could be overcome by further safe handling procedures and the assessment of present facilities to reduce the risk of any spills and leaks, there remains a growing public concern with regard to the use of oxygenates in gasoline fuels. In an effort to balance the need for lower emission gasolines and concerns about the use of oxygenates it, therefore, would be of great benefit to the industry if a cleaner burning gasoline without oxygenates could be made. A cleaner burning gasoline resulting in low NOx emissions would be of particular benefit to the environment in light of the increased attention to reducing nitrogen oxide emissions. The availability of such a gasoline, which contained substantially no oxygenates, would allow the public to realize the environmental benefits of low emissions, yet ease the concern of potential contamination of ground waters, and the environment in general, with oxygenates. Of benefit to the industry would also be such a low emission, gasoline which contained substantially no oxygenates and also offered more flexibility to refiners in blending the gasoline.
Accordingly, it is an object of the present invention to provide a gasoline fuel which can truly benefit the environment and offer good performance.
It is another object of the present invention to provide a gasoline fuel which provides good emissions, yet is substantially free of oxygenates.
Yet another object of the present invention is to provide a low-emission, substantially oxygenate-free gasoline fuel which exhibits surprisingly low NOx emissions when combusted in an automobile internal combustion engine.
Still another object of the present invention is to provide a gasoline fuel which provides good emissions and also permits more flexibility to refiners in blending the gasoline.
These and other objects of the present invention will become apparent upon a review of the following specification and the claims appended thereto.
In accordance with the foregoing objectives, the present invention provides an unleaded gasoline fuel which is substantially free of oxygenates, i.e., the fuel contains less than 1.0 weight percent oxygen based on the total weight of the fuel composition, and most preferably contains no oxygen containing compounds. The gasoline fuel of the present invention also has a Reid vapor pressure of less than 7.5 psi, a sulfur content of less than 30 ppmw, and more preferably less than 20 ppmw sulfur. The fuel of the present invention also has an aromatic hydrocarbon content greater than 30 volume percent and/or a 50% D-86 Distillation Point greater than 220xc2x0 F. and/or a 90% D-86 Distillation Point greater than 330xc2x0 F. The gasoline fuel preferably also has an olefin content of 8 volume percent or less, and more preferably 5 volume percent or less. It has been found that such a gasoline fuel offers substantially oxygenate free gasoline which avoids the environmental impact of oxygenates, yet when combusted in an internal combustion automobile engine provides good performance and good emissions.
In particular, surprisingly low NOx emissions have been observed for the gasoline fuels of the present invention, with the NOx emissions being substantially lower than that predicted by the California Predictive Model established by the California Air Resources Board (CARB). Good performance with surprisingly low NOx emissions is obtained despite the fact that the gasoline fuel of the present invention does not meet the specifications for the CARB reformulated gasoline fuel. The gasoline composition of the present invention is substantially free of oxygenates, and it also exceeds the cap limits set for at least one, if not more, of the properties regulated by the specifications for the new (Phase 2) reformulated gasoline. Nevertheless, despite not meeting the specifications for properties required by CARB for reformulated gasolines, the gasoline fuel of the present invention allows one to enjoy good emissions, and particularly surprisingly low NOx emissions, while also avoiding the potential problems of oxygenates. For it has been surprisingly found that when one controls the amount of sulfur in accordance with the present invention to less than 30 ppmw (and more preferably less than 20 ppmw), and in particular controls the amount of sulfur together with olefins in accordance with the present invention to no greater than 8 volume %, it is possible to have flexibility with respect to the other regulated fuel properties in a non-oxygenated fuel without sacrificing low emissions.
In another embodiment of the present invention, there is provided a method for operating an automotive vehicle having a spark-ignited, internal combustion engine. The method comprises introducing into the engine an unleaded gasoline which is substantially free of oxygenates in accordance with the present invention. The unleaded gasoline is then combusted in the engine. In a preferred embodiment, the automotive vehicle also has a catalytic converter into which at least some of the engine exhaust emissions created by combusting the unleaded gasoline are introduced, with the resulting emissions then being discharged from the catalytic converter and subsequently to the atmosphere. Good performance and surprisingly low NOx emissions are realized upon using the unleaded gasoline of the present invention in the operation of an automobile.